Recently, a digital radiography (DR) that uses an X-ray image detection apparatus such as a flat panel detector (FPD) for converting X-rays into digital data has been practically used. The X-ray image detection apparatus has been rapidly distributed since it has a merit in that an image may be immediately confirmed, as compared to a conventional computed radiography (CR) method that uses an imaging plate.
As the X-ray image detection apparatus, various types have been proposed. For example, there is an indirect conversion type which converts X-rays into visible light using a scintillator such as CsI:Tl, GOS(Gd2O2S:Tb) first, and converts the converted light into electric charges which are accumulated in a semiconductor layer. The indirect inversion type X-ray image detection apparatus includes a scintillator and a photodetector having a semiconductor layer.
In such an X-ray image detection apparatus, for example, in a case of being used in a living body, it is preferable to lower the X-ray irradiation dose, and a scintillator with a high luminescence amount and an excellent sensitivity is required. Thus, in order to increase the luminescence amount in the vicinity of the photodetector, there is proposed an X-ray image detection apparatus configured such that a phosphor such as CsI is deposited on a glass substrate of the photodetector and X-rays are irradiated toward scintillator from the photodetector side (see, e.g., Patent Literatures 1 and 2).
Here, in theory, as the thickness of the crystal phase of the scintillator is increased, the sensitivity is improved. However, in practice, when the thickness of the crystal phase is increased beyond a limit, there is a problem in that light may be attenuated or disused when passing the scintillator and thus, sufficient sensitivity may not be obtained or blurring of an image may occur. For this reason, an aggregate of columnar crystals that guide light emitted from a phosphor is used (see, e.g., Patent Literature 3). Since the light is guided in the thickness direction of the panel of the scintillator by such columnar crystals and incident on the light director, the sharpness of a detection image is improved.
In order to enhance the adhesion of the columnar crystals and a support, it has been proposed that several cover layers made of a phosphor host are laminated and formed between the columnar crystal and the support so that the coverage rate of the support is 95% or more in Patent Literature 3. Patent Literature 3 presumes an imaging plate as described above and is not related to an FPD.